Electric Bike Lithium Battery Primer

If your looking for a ready-to -buy lithium ebike source check out Luna Cycle for the packs and the supplier we recommend.

Whether you’re shopping for a turn-key commercially available electric bike, or trying to find or build a good battery for an e-bike conversion, being able to find the right battery for an electric bike is a difficult task. The right battery pack is the most difficult part of the e-bike equation. Keep in mind that even if you’re buying a turn-key electric bike, the lithium battery is more than likely the most expensive component in it, and…not all lithium batteries are created equal, so you should know what you are getting before you buy the ebike.

Lithium electric bike batteries are not cheap, they are not perfect, and they are not readily available. Some OEM’s such as BionX sell a moderately sized lithium e-bike battery pack for $1000 plus. Optibike sells their touring LiPo battery as an add-on accessory for their bike for a gasping $2500. It is surprisingly difficult to find a ready to plug in LiPo battery pack for sale on the internet by any real company. The reason is simply product liability.

Lithium Battery technology in a bicycle is still experimental and you have to use a lot of common sense when using these batteries. However with a little education and some end user carefulness, you can use lithium batteries safely, the same as you can safely deal with putting gasoline in your riding lawn mower.

$2500 optibike touring LiPo battery

Lithium batteries and hazardous shipping

Recently the federal goverment has been cracking down on the shipping of lithium batteries. For the vendor, it means that they must have Hazardous Materials (hazmat) shipping and pay hazmat charges, and only can ship an officially tested hazmat-compliant battery. This adds considerably to the cost of lithium batteries, and makes it even harder to find an ebike dealer, who will sell you any lithium battery pack that they can affordably source.

Ready-Made Lithium Packs

For people who are new to the hobby, ready-made lithium packs are the way to go. Several manufacturers offer ready to go Lithium packs with a built in Battery Management System (BMS) at affordable prices.

The most noteworthy battery supplier is based in the USA and is offering lithium packs based on high quality cells. A new vendor in 2015 is Lunacycle.com , so…check them out for a multitude of different packs at a very reasonable price.

You can buy LiFePO4 straight from China from Ping Battery. These batteries are a little bulky, but are safe, and will last over 1000 charges. You can also buy ready made Lithium Iron Phoshate (LiFePO4) or Lithium Polymer (LiPo) packs from BMS battery.

A high quality USA battery manufacturer by the name of “Allcell” constructs packs consisting of 18650 cells (cylindrical cells that are 18mm diameter and 65mm long) and uses high tech packing materials to spread out the cells and thus the pack gets a longer life. This is the pack of choice in many high end commercially available ebikes including the Optibike, the Picycle, and the Hanebrink. (click on each to see article on that electric bike). The 18650 battery cell format is mass-produced for laptop computers and cordless tools.

When you buy a ready made pack they have a BMS which balances each cell automatically and they can be charged with a purpose made bulk charger such as the luna charger.

Buy a ready made LiPo battery, or build your own?

DIY Hobby Pack with no BMS

Lipo batteries are currently the “hottest” battery choice for electric bike enthusiasts. LiPo batteries are the most power-dense type of battery available to electric bike riders today. The problem is that LiPo battery packs for e-bikes are hard to find, especially one with high output if you are building a racing bike for riding off road.

If you want a LiPo battery pack, one of your better choices if you want to save money and have a lot of output amps is build one of your own from a Hobby King packs. This requires a lot of time and knowledge, not only in building the pack but also in managing it. LiPo batteries can be extremely dangerous and prone to burst into fire if not assembled with a lot of precautions (BMS) and cared for properly.

Essential for either building or buying a ready made pack is deciding how large of pack you want and how much you are willing to spend on that pack in terms of weight and price.

Most of the price involved these days in building an e-bike or buying a ready to go e-bike is the size and chemistry of the battery pack. For the consumer its important to understand the difference between a 24V, 36V, and 48V pack. Also know what a 10-Ah pack is compared to a 5-Ah pack.

A 48 volt 20-Ah pack contains 960 watt hours and once you get close to 1000 watt hours you are getting serious commuting range which most e-bike manufacturers promise but do not deliver…think 30 miles.

When you are comparing packs of different voltages calculate watt hours to see how much you are getting for your money…especially when buying a turn-key e-bike.

How big is the battery I am buying?

Your battery pack size is based on voltage and amp-hours. The higher the voltage and the higher the amp hours of your battery, the more range your battery will give you. A 48V 10-Ah pack gives you 480 watt hour (48 X 10). This gives you an easy way to determine exactly how much battery you are buying. The wattage of a battery is the only accurate determinant to judge what range your finished ebike will have.

How powerful is the battery?

Different batteries have different amperage capacities. Most cheap lithium batteries are not capable of putting out much amperage. If you have a 48 volt bike that performs well when using 25 amps, you are going to want a 48 volt battery that has close to a 20-Amp-hours or more. If you want to eventually hot rod your ebike (read our hot rod hub motor primer here), you may want to invest now in a high amperage battery. This will “future proof” your system by paying a little bit more now for the battery, but then you can program more performance from the controller in the future, if you want…

The other thing to consider is that if you have one 48-volt 10-Ah battery putting out a measly 20 amps, you can add a second version of the same battery, wire them together in parallel, and you will have a 20-Ah pack with a 40-amp capacity, thus effectively doubling your range and doubling your amp output performance.

When you buy your battery, make sure you know what its maximum amp output is. Remember, by multiplying amps and voltage you get the actual current capacity of the battery. For example a 48-volt 25 amp pack can put out 1200 watts.

What is the chemistry of the battery you are getting?

Lithium chemistry is considerably more expensive than the “old school” lead acid chemistry. If you are buying a battery pack or a bike that already has a battery pack, be familiar with the chemistry that you’re buying. For example, its hard to find a good e-bike for under a thousand dollars with a decent-sized lithium pack. Lithium is pricey. Be realistic in your expectations when e-bike shopping on how much the electric bike will cost compared to what kind of range, performance, and life expectancy you will get out of a lithium battery pack.

What format are the soft cells? Hard or soft shell? Big or small?

When choosing a battery for your bike, not only is the weight important but the volume is also important. You want your pack as small as possible so its easy to stow and easy to hide. So therefore you should consider you battery’s volume, not just its weight. For sure you need to go with a lithium chemistry and not an old school heavy and large Sealed Lead Acid (SLA) or Nickel-Metal Hydride (NiMH) chemistry.

There are two prevalent ideas in pack constructing in these modern days…one is to use larger pouch-like soft cells to construct the pack. The stealthiest battery chemistry by far is LiPo, large cells with power-dense cobalt in the anode chemistry, such as what comes in Hobby King cells. Here is what I mean by “large cell” LiPo. These are soft pouches and large. When you use a pack made of these it will consist of fewer wired together cells than if you use small cylinder cells.

When you buy a Hobby King pack, it will have a number of these large cell LiPo’s strung together like this 6 cell in-series (6S) pack. The big downsides of this pack is that it will only last you in best case maybe 300 charges and it is volatile, and susceptible to possible fire if not well managed and cared for. When using cobalt-based LiPo, it is best to use some kind of BMS, and also you should charge it in a safe location.

Here is a an example of a large format soft pouch LiPo pack with 13 cells, and a BMS. This pack was built using cobalt LiPo soft cells with a BMS from a Chinese factory for an electric bike. You can see the top cell has been squished, causing the cell to fail and the BMS to shut down the battery, and not allowing it to charge or discharge. This pack is small and light (7lbs). This $500 pack is now ruined, but all is not lost since it did not start a fire, and it did NOT take the house with it.

This is what I refer to “small cells”, the 18650 (cordless tool) type cells which need to be spot-welded or soldered together to form a large pack. The big advantage of these cells is they offer better cooling because of the nature of their shape to the LiPo soft pouches, and therefore have the capacity to last longer.

Also, since the negative electrode is the entire bottom and sides of the cell (formed by a metal cylinder) these cells can take some bouncing around. Be aware if you scratch the plastic wrap on the cylinder, the metal shell underneath is energized to the negative electrode, so…an electrical short may be possible.

How fire safe is the battery?

Lithium batteries are not 100% fire-safe. Some batteries are more dangerous than others, depending on the chemistry, whether it has BMS or not, and what kind of casing the battery is in. If the battery is cased in metal its less likely to burn your garage down, than if its encased in plastic. Also be aware that all BMS’s are not alike, some are good and others are crap, just like anything else in life.

Have a plan on where you are going to charge your bike before settling on a battery chemistry. If you live in a crowded apartment building and the only place you have to charge is in your living room floor, you may want to decide against any of these lithium technologies.

Sealed Lead Acid (SLA)

Old school SLA batteries

This is the old technology for e-bikes that is heavy as bricks and does not have longevity. Lead acid will double the weight of your electric bike. Unless you have to because of money restraints, we advise to steer way clear of lead acid batteries. Your bike will have a completely different feel and range if you spend the money on one of the new lithium technologies.

Nickel Metal Hydride (NiMH)-

An older battery technology that was popular around 10 years ago as replacment for lead acid in some more expensive commercially available e-bikes. Today it has been obsoleted in e-bike applications because of the recent availability of LiPo and LiFePO4 cells. NiMH is a finicky technology to deal with. The packs do not have long life expectancy, and have to be treated delicately. One big problem for DIYers is that its very hard to safely charge NiMh cells that have been soldered together in parallel. Extra care is needed for NiMH in both assembling and charging.

LiFePO4 –

24V, 36V and 48V commercially made e-bike packs from China

Lithium Iron Phosphate is currently the most common lithium battery used in Ebike applications. It is considered the most stable lithium battery type available today (low risk of fire) and has a reasonably high life expectancy of over 1000 charges.

For a complete write up on LiFePO4 care and trouble shooting read our story here. LiFePO4 cells nominal voltage is generally from 3.0-to 3.2 volts, and generally, lifepo4 is a heavier and less power dense than available LiPo batteries and is not capable of as high of amperage discharge.

LiFePO4 is currently widely available for purchase as e-bike packs complete with BMS on ebay and other online merchants. Mostly it is sold by small companies. Also, most of the commercially available e-bikes powered by lithium batteries are using the LiFePO4 chemistry.

A123 LiFePO4 Cells

A123 is a brand name of lithium ion phosphate battery used in many EV even full car applications.. A123 cells are known to be of high quality and capable of having high-amp discharge rates with long life expectancy of over 1000 charges. They can provide large amounts of power and have been used in racing applications as well as electric car builds. Chrysler has chosen to use A123 cells in their electric cars.

Small hard-cased A123 cells (about the size of a “C” battery) have been salvaged out of power drill packs, car battery packs etc, and have made it into the hands of e-bike DIYers who solder them together in series and in parallel to construct a pack big enough and powerful enough to power an e-bike.

A123 battery pack from a factory

A123 cells are 3.3 volts per cells (nominal).

Recently, A123 has released a large 20-Ah LiFePO4 pouch cell with the EV market in mind.

A123 20-Ah 3.3v

LiPo-
Lithium Polymer cells, used mostly in the e-bike community to describe soft-pack RC like cells, generally have a lighter weight per watt-hour, and they have a high percentage of cobalt in its anode, which makes them very power-dense (lots of amp-hours in a small package) and also capable of very high amps of discharge (for high performance). Single cell LiPos are connected together in series to form a battery pack.

The word “polymer” in its name merely means the electrolyte is a gel instead of a fluid or solid. We use the term LiPo because that is what most catalogs call them when you are shopping for them.

Common lithium cobalt oxide (LiCoO2) batteries can catch fire or explode during loading and even when just stored. The safety depends on user precautions and the quality of the Battery Management System (BMS).

Golden Rules of proper use of Lipo:
NEVER discharge a Lithium Polymer battery below 3.0V
NEVER charge a Lithium Polymer battery above 4.2V
NEVER puncture a Lithium Polymer battery

LiPo homebuilt with BMS

BMS (Battery Management System)

A lot of DIY’ers these days are making the extra effort to install a BMS in their home built batteries. Adding a BMS is the way to go if you want your battery to be fire safe. BMS’s can range from a simple hobby king cell log with an audible alarm if the pack gets too low or too high, to an expensive custom-made BMS complete with pack shut offs.

There is a plug and play BMS available for hobby king packs and can be found here.

Cell logs plus a low voltage alarm creates basic BMS.

An expensive and comprehensive BMS…this unit costs $200

LiPo packs that are homebuilt (without a BMS) can be extremely dangerous if you do not approach your battery with a lot of knowledge and care. Be sure to research extensively before building such a pack. Many E-bikers construct packs with no BMS using Turnigy/Zippy packs, acquired cheaply online through the Hobby King company which is based in China. For those who risk running their batteries without BMS they still use sophisticated chargers to balance their packs and constantly monitor the health of their cells.

RC Charger and lipo packs

If you are thinking about building your own LiPo pack, a 48V / 10-Ah battery pack can be made for around $300. However to undertake this project you should research extensively on www.endless-sphere.com on how to build and take care of your pack. Expect hours of reading before you are ready to build a pack of your own.

Electricbike.com will soon be providing articles on how to build and maintain a high performance LiPo pack.

Safe Guarding a LiPo fire with a metal battery enclosure:

One of the simplest safe guards you can take is to contain your LiPo in a metal box so that if it does break-out into flames, the fire will be contained in a metal enclosure.

The only two ebike companies that sell LiPo to the public are Optibike and Pi-cycles, and both contain the battery in a strong metal box which makes up of the frame. The companies fire tested these enclosures and are confident that their frame are effective and safe vessels for LiPo storage.

You too can find a metal box to store your batteries in while riding and charging. Here is an example of a custom built metal box that holds six hobby king packs perfectly (make certain to add a vent so pressure does not build up if a pack goes into flames!):

Most of the problems occur when charging an ebike because they are unsupervised and that is when a LiPo fire can burn down a house etc. Use common sense on where you are going to charge your bike or battery pack, so that if it does burst into flames it does not take your house with you. I have a big steel barbecue grill set up in my entryway which I charge my battery packs in as nice safeguard. This involved taking the battery pack out of the bike after each ride but I am OK with that:

Another option is to simply charge your LiPo battery in your home oven:

Whats the worst can happen with bad lithium battery choice and mis-management:

Check out this video of what happened when the girl in the above picture out on a ride, did not treat her LiPo battery with care and diligence:

The Future of LiPo

In 2012, the future of LiPo in e-bikes looks bright. Most large EV manufacturers are focusing on LiPo as the lithium battery power of the future. LiPo technology is developing fast and becoming safer, more reliable, cheaper, and with a higher life expectancy. Since LiPo cells are being developed to be safer, more efficient and more economical (mostly for main stream products such as the automobile) the electric bicycle industry will be able to piggy-back and utilize the newly available technology at an affordable price. Currently, the latest “best” chemistry involves Manganese-Cobalt which is a lot more stable than the cobalt chemistry of the past.

Look for big improvements in LiPo batteries in the near future, and better availability and more affordability. The one big “if” on the future of LiPo is how easy and expensive it will be to ship.

Eric has been involved in the electric bike industry since 2002 when he started a 6000 square foot brick and mortar Electric Bike store in downtown San Francisco. He is a true believer that small electric vehicles can change the way we operate and the way we think.

Option 2 has a lot going for it. Especially if you trade off the lighter weight for more capacity. eg 36v15AHr LiNiCoMn instead of
36v10AHr LiFePo for the same weight and price.

I’m deeply uncomfortable with recommending RC LiPo from the likes of Turnigy for people who don’t know what they’re doing. The above 3 options are plug and play and require no special skills. And they’re essentially safe when bulk charged with the associated charger.

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craig

( October 19, 2012 )

hi i was considering adding a second set of batteries to my ebike in parallel to double the range but heared on a thread somewhere that this can damage/overload the controller which i suspect is a load of tosh but can anyone confirm/clarify this as i assumed the amp hour capacity was just that and the max amp output was just that, the maximum that can be drained at once, my understanding is it doesnt matter what amp hr the pack is as the amps drawn into the controller is governed by the demands of the motor which wont change if i have 2 packs connected.
and i also have another question if i charge the 2 packs seperately then connect them to my bike in parallel do they both have to have the same capacity and the same wear for instance i currently have 2 sets of batteries (sla’s) one of which is an old set at half original capacity or there abouts and the new ones hold the full charge so can they be connected together to give me 1 1/2 x my range? or if im going to put a double pack on do i have to use and charge them together so theyre all at the same state of charge and wear the same as ideally i would like to only have to carry a second pack when i require the extra range.
my questions are obviously related to sla’s as this is what i have now but if answers differ according to battery chemistry i would like to know this as well for future reference any info much appreciated cheers craig

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ElectricBIke

( October 20, 2012 )

craig it should not damage your controller. When you connect two batteries together in parallel it will actually extend the life of both batteries because you are not taking as much of a toll on them when discharging and hopefully not running them down as low.

SLA’s you dont have to worry about….you can connect them together and charge them together or separately it doesnt matter. Just keep them charged, charge as soon as possible after riding.

tjcooper

( September 2, 2014 )

Please see the video’s on RCgroups under LiPo fires. A simple 2200maH 3S battery pack blew the lid off a secured 55caliber ammunition can. Putting a LiPo pack in a closed metal case is a real “bomb” waiting to happen. See all the videos on RCgroups that show what happens when a battery is over-charged or over-discharged inside air-tight causes. The real solution is to make the case have a “preferred direction” of discharge……which can be very powerful. This is done by drilling holes in the case. But it stops the explosion factor. The best thing is to have a BMS on or inside the battery. Even if the cheapy Hobby King voltage monitor, that is much better than nothing at all. Also consider putting in a voltage monitor that has a temperature guage attached. When ever the pack skin gets above 85 deg C, you are in real danger of “vent and flames”. The temperature and voltage are that two big things that can make your battery pack safe………….also store the pack where if it does go to “vent and flames”, no human being will get burned.

The new LiPo in the plastic wrap are much better than 10 years ago….but they still can go ballistic if mishandled. Always treat them as a hand grenade with a pull pin that is “on the edge”.
Dr. Ted J Cooper

( December 20, 2012 )

6 months on and some changes.
– http://www.greenbikekit.com/ are selling almost exactly the same kit as BMSBattery but with cheaper shipping. Slightly weird as they appear to be related companies or perhaps even the same company.
– BMS/Greenbikekit are now selling cased or shrinkwrap LiFePo batteries based on high capacity cylindrical cells probably from Headway and with a BMS. These have a higher C Rating between 5C and 10C. This makes a 48v-10AHr battery useable in a high performance kit with 30-40A max. Using this with a 1000W-1500W motor/controller should work fine. This is heavier than LiPo but close to the holy grail. Long lasting, safe/easy/convenient, high power.

Note that in the article it says that LiFePo is the most commonly used chemistry. I think that depends on where you are looking. I suspect that LiNiCoMn or the older LiMn is actually most common in terms of total unit cells because they’re the cheapest and get used in the low end E-Bike market in China.

( March 5, 2013 )

I’ve been using this for a year, and the batteries are near the end of there lives, so I’m thinking of upgrading the battery to Lipo4.

The two thing I’ve learned from this article is

1. I still have hours and hours of more reading to go before I attempt anything to stay safe, and
2. I now have plans for that old barbeque that’s just been taking up space in the garage. Thanks again!

diggler

( March 24, 2014 )

Hi I need help! I am building my own battery pack from old laptop batteries (18650’s). I bought the cheep $250 48v 1000w ebike conversion kit on ebay. I have many questions! It seems the perfect number of cells to connect in series are 13! This is a big problem for me because I am cheep and I already bought the Imax B6 battery balancer charger. I also bought 7x 6s balancer leads and 5x 4s leads. The Imax has a max charge voltage of 22.2v (so it sais in the manual), and a max balance of 6 cells at once. I also bought the parallel balance charging board. I don’t want to charge two or three packs at once to just have to turn around and charge one separately. So now I’m faced with the decision of making a 12 series battery or a 15 series battery (I will buy 5s leads in this case). The problem is with the 12 series battery the nominal voltage is only 43.2. Or a 15 series battery with a nominal voltage of 54. Which I’m pretty sure is a big no no because the controller is only meant to handle 48v within reason (13s max charge voltage of 53.3 and 12s 49.2 at 4.1 v per cell). But if I make it a 12s, running around most of the trip at 44v, will this drain the Amps faster because the motor wants 48v? I’m thinking no but just wanted some confirmation on that and if the controller can handle more volts. I could make a 15 series batter and just charge to 3.6 or 3.7 volts. Is this hard on the cells?

Thuong

( January 15, 2015 )

francisc

( February 2, 2015 )

hello. I have a KTM bike-trail’s 2013 model. I have problems with the battery. I had the bike wheel and I bought one original ktm 26V from the company. defect occurs so: I put the plug on the charger to charge the battery and flashing green LED lights and red and it is immediately interrupted – interrupted flashing red and the buzzer sounds and noises that can fix … ? Please help me if you know how. sorry for my English but I used google translator

In the event that someone tried to load another source battery charger – this battery has higher voltage protection ??

( November 18, 2015 )

Andrew Mathison

( February 7, 2016 )

Firstly, I am very grateful for the large amount of useful information you have given us here, basically for free.

It cannot get any cheaper than that!!! Many thanks.

But having read through the document mostly, not completely, I simply stopped reading further due to incorrect usage of words and many bad spellings, some of which would not be caught by a spell checker – “table” for “stable” for example.

But there were also terrible misleading, misuses of words like:-

Golden Rules of proper use of Lipo:

NEVER discharge a Lithium Polymer battery below 3.0V – Battery is wrongly used here for “CELL” I believe, discharging a “battery” to 3.0V, if possible, would ruin the WHOLE Battery, as a minimum.

NEVER charge a Lithium Polymer battery above 4.2V – same error

NEVER puncture a Lithium Polymer battery – same error I feel.

I know what is meant, but there are maybe online readers who will take your online document at “face” value and end up with some expensive and possibly dangerous situations…..